1. Technical Field
The present invention relates to a lubricant impregnated in bushings comprising of a metal sintered body and to an oil-free chain being used for power transmission mechanisms, transport mechanisms, etc. and constructed so that the bushings make sliding contact with pins in a state that the lubricant impregnated in the bushings oozes out without additional lubrication.
2. Description of Related Art
Conventionally, chains such as bushing chains and roller chains are used for power transmission mechanisms and transport mechanisms. A bushing chain is constructed so that a pair of outer link plates connected to each other using two pins in both ends and a pair of inner link plates provided with two bushings in both ends, the two pins on the adjacent sides of two pairs of outer link plates being fitted in the two bushings, are connected alternately. In the case of a roller chain, rollers fitted on the bushings are further provided.
An oil-free chain is known which is constructed so that oil-impregnated bushings comprising of a sintered body impregnated with a lubricant are used as the bushings of the chain constructed as described above and so that the oil-impregnated bushings make sliding contact with pins in a state that the lubricant impregnated in the oil-impregnated bushings oozes out without additional lubrication.
Japanese Patent Application Laid-open Publication No. Hei 11-140478 discloses an invention relating to an oil composition for sintered oil-impregnated bearings, produced by blending 0.01 to 3.0 wt % of carboxylate ester and/or organic zinc sulfonate serving as a rust inhibitor with base oil.
In Japanese Patent Application Laid-open Publication No. Hei 11-140478, in the case that poly-α-olefin (PAO) or a hydride thereof is used as the base oil, it is assumed that the average molecular weight of the PAO is in the range of 200 to 1600, preferably 400 to 800.
In addition, Japanese Patent Application Laid-open Publication No. Hei 9-125086 discloses an invention relating to an oil composition for oil-impregnated bearings, comprising base oil containing polyolefin and polyol ester, wherein the weight ratio of polyolefin to polyol ester in the above-mentioned base oil is in the range of 20/80 to 80/20.